Technical Field
Embodiments described herein relate to a support apparatus for balance correction, where in making balance corrections of a rotating rotated body such as a rotor of a turbocompressor the support apparatus rotatably supports the rotated body using a vertical mandrel.
Description of the Related Art
With a rotating rotor (which corresponds to a rotated body according to the present application) of a turbocompressor, to solve imbalance (dynamic unbalance) caused by part tolerances during production, conventionally, an amount of the imbalance is measured and then the imbalance is corrected using a balance correction apparatus.
To measure the amount of imbalance with high accuracy, the balance correction apparatus uses a support apparatus (support apparatus for balance correction) adapted to rotatably support a rotor alone using a vertical mandrel. Regarding the mandrel, in many cases, as disclosed in Japanese Patent Laid-Open No. 2005-172537, a columnar mandrel fitted in a support hole located in a rotation center portion of the rotor is used, the support hole having a circular cross section, and the mandrel is structured such that a fluid radial bearing will be provided on an outer circumferential surface of the mandrel and that a fluid thrust bearing will be provided on a base end side of the mandrel.
With this structure, when the support hole in the rotor is fitted over the mandrel, the entire rotor is put on the mandrel. Subsequently, as a fluid (e.g., air) is ejected to an inner surface of the support hole through an ejection hole in the fluid radial bearing and the fluid (e.g., air) is ejected to an opening edge portion of the support hole through an ejection hole in the fluid thrust bearing, the rotor is rotatably supported around the mandrel while floating.
To measure the amount of imbalance (amount of dynamic unbalance), the rotor is rotated by giving a turning force from outside to the rotor in a floating state, for example, by ejecting a driving fluid (e.g., air) to blades, and then behavior of the rotating rotor is measured using various sensors provided on the balance correction apparatus.
However, the rotor is supported by the fluid radial bearing in a radial direction of the rotor in a small area in lower part of the rotor and the rotor is supported by the fluid thrust bearing in a thrust direction of the rotor in a narrow area compared to an outside diameter of a workpiece. Consequently, when the amount of imbalance of the rotor is excessive, the rotor inclines and measurement accuracy of the amount of imbalance degrades, making it difficult to measure the amount of imbalance properly. In the case of a rotor liable to cause excessive imbalance, in particular, i.e., a rotor whose center of gravity position is higher than a position at which the rotor is supported by the fluid radial bearing, the measurement accuracy tends to degrade.